[Effects of Fertilizer Application Strategy Adjustments on Nitrogen and Phosphorus Loss from Typical Crop Systems in Taihu Lake Region].

The intensity of crop farming fertilizer input is generally high in the Taihu Lake Region, with chemical fertilizer as the main form. Due to inappropriate fertilizer application, nitrogen and phosphorus loss have occurred, causing serious agricultural non-point source pollution. The Ministry of Agriculture and Rural Affairs of China has launched the "zero-growth action for chemical fertilizer use" and "replacement action with organic fertilizer" ("two actions" for short) campaigns since 2015. Local agricultural sectors adjusted fertilizer application strategies of crop farming to respond to the call of two actions. However, the current research is still focusing on reducing the total amount of fertilizer application and increasing the area of organic fertilizer application, which is mainly based on grain crops. The study of agricultural environment problems is still lacking, especially in vegetable, orchard, and tea systems. Therefore, a study was carried out in the typical agricultural area of Suzhou City Wuzhong District from 2019 to 2021. Based on the data of the amount of nitrogen and phosphorus removal by harvest crops and soil nitrogen and phosphorus residual in paddy, vegetable, orchard, and tea systems, the loss was estimated. The responses of nitrogen and phosphorus loss from typical crop systems to fertilizer application strategy adjustments were studied through analysis of different factors. The results showed that fertilizer application rate was the key to control nitrogen and phosphorus loss. Additionally, the suitable replacement ratio of organic fertilizer could further reduce the loss risk. It should be noted that the urgent demand for nutrients in crop growth should be considered to determine the timing of organic fertilizer application, and agricultural machinery should be used to assist organic fertilizer application to reduce labor output if possible. Fertilizer efficiency was the core of environmental friendliness and economic benefits of crop farming. Hence, improving fertilizer efficiency should be the guidance of fertilizer application strategy adjustment. Our suggestions on the adjustment of fertilizer application strategy in different crop systems in the study area are as follows:attention should be paid to the nitrogen, phosphorus, and potassium input ratio in paddy systems to further reduce nitrogen and phosphorus loss. Planting structure adjustment should be emphasized in vegetable systems to promote fertilizer efficiency. The strategy to satisfy both tea and orchard growth from a composite system perspective would help to build crop systems that meet the needs of green agricultural development.